Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 07-23-2014, 01:35 PM   #1
Newbie
 
Join Date: Jul 2014
Posts: 7
Rewards Points: 10
Default

Heat Pump A/C Performance Expectation


I have a Trane outdoor Air to Air heat Pump, it's about 2 years old, running on the old R22 refrigerant, with an older 1999 trane electric furnace for backup.

I had the HP unit moved a month ago from the front of the house to the side, and I am checking that the system is working "correctly" post move, before heating season starts. The unit was moved about 10 feet closer to the house than it was before. The unit was 'drawn down' by the repair tech before the move, and re-charged from the unit after the move, and after passing a 250psi pressure test verifying that all soldering work was fine.

So, I turn the system on to 'cool' to see everything is fine. House and Outside temp, around 75 degrees F. Hp fires up, and after a half hour, I measure the insulated copper pipe temp entering the furnace coil - it's around 65 Degrees F, and the air discharge stream from the HP outside is around 85 degrees, or so. Is this in the range of what I can expect from the system performance wise when cooling? I was expecting to see a much lower cold feed into the furnace than what I measured. The pipe has been completely re-insulated by the way so shouldn't be losing temp from the HP to the furnace.

Curiously, when I call for heat, the pipe 'feed' seems to get quite a bit hotter, so on the heating side it seems to work 'better' . Didn't measure those temps, but I could do so.

So, is it possible that the system has lost some refrigerant in the move, and it should be re-filled from scratch? Or is there nothing wrong with only a 20 degree differential such as I was measuring in summer cooling mode?

Thought I would ask here before forking out the $$ for the tech to come back and test.

John

J_Manson is offline   Reply With Quote
Old 07-23-2014, 01:44 PM   #2
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 9,628
Rewards Points: 2,394
Default

Heat Pump A/C Performance Expectation


The best way is to measure the supply air temp in the supply duct about a foot downstream from the indoor coil and subtract it from the return temp in the return duct or the house temp at the thermostat. Should be from 16-20 deg drop. If not it may be low on Freon. Rule of thumb for discharge air temp is it should be 15-20 deg higher than the outdoor temp. 75 + 15 = 90 so I suspect you are low on Freon.

There may be a Freon leak at the service valve caps at the outdoor unit as they can be tricky to seal. Get him to check there first and the schraeder valves where he attaches the gauges.

__________________
"Cut it twice and it is still too short".

Last edited by yuri; 07-23-2014 at 01:46 PM.
yuri is online now   Reply With Quote
Old 07-23-2014, 02:27 PM   #3
Member
 
Join Date: May 2014
Location: MO
Posts: 72
Rewards Points: 75
Default

Heat Pump A/C Performance Expectation


Yes 20* differential is very good, can't ask much more out of the A/C.
Bitters is offline   Reply With Quote
Old 07-23-2014, 02:48 PM   #4
Newbie
 
Join Date: Jul 2014
Posts: 7
Rewards Points: 10
Default

Heat Pump A/C Performance Expectation


Quote:
Originally Posted by yuri View Post
The best way is to measure the supply air temp in the supply duct about a foot downstream from the indoor coil and subtract it from the return temp in the return duct or the house temp at the thermostat. Should be from 16-20 deg drop. If not it may be low on Freon. Rule of thumb for discharge air temp is it should be 15-20 deg higher than the outdoor temp. 75 + 15 = 90 so I suspect you are low on Freon.

There may be a Freon leak at the service valve caps at the outdoor unit as they can be tricky to seal. Get him to check there first and the schraeder valves where he attaches the gauges.
Thanks Yuri, I will get a better thermometer, and measure inside the air plenum, both in cooling as well as heating modes. Question, am I looking for a 15-20 degree differential between the return duct and downstrem of the HP coil, or a 20 degree differential between the outside temp and downstream? On startup, they would be the same as the house temp is the same as outside initially at least, in summer. I am sure I won't get that 15-20 degree differential, the pipe coming in was only about 10 degrees below ambient when I measured it... So It has probably leaked some...
J_Manson is offline   Reply With Quote
Old 07-23-2014, 02:54 PM   #5
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 9,628
Rewards Points: 2,394
Default

Heat Pump A/C Performance Expectation


The supply temp diff is the one Pro's use ( along with Freon pressures etc ). For a DIYer that will give you a rough idea.

The outdoor temp rise will vary and the newer higher SEER units with larger coils will be lower than an old school unit.

The supply temp diff is what you want. The house temp ( return temp ) - the supply temp = how much cooling you are getting.

There are other variables like whether the inside and outdoor coils are clean, duct size, fan speed but in your case start with the temp diff.
__________________
"Cut it twice and it is still too short".

Last edited by yuri; 07-23-2014 at 02:56 PM.
yuri is online now   Reply With Quote
Old 07-23-2014, 03:30 PM   #6
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,578
Rewards Points: 2,836
Default

Heat Pump A/C Performance Expectation


In cooling mode. The large pipe does not feed the indoor unit. It is returning cool gas to the outdoor unit.
__________________
When posting in certain forums, knowing your location will help others give better feedback/advice/solutions to your questions.
beenthere is online now   Reply With Quote
Old 07-23-2014, 08:27 PM   #7
Newbie
 
Join Date: Jul 2014
Posts: 7
Rewards Points: 10
Default

Heat Pump A/C Performance Expectation


OK, the cooling differential is about 7 degrees F, and when in heating mode, the differential is about 23 degrees F. Any reason why the cooling system's performance is 3 times worse than the heating performance?? The small dia pipe is NOT insulated, so if it's the one delivering cooling to the unit when in cooling mode, insulating that pipe may make a difference?

Thanks guys!

John
J_Manson is offline   Reply With Quote
Old 07-23-2014, 08:32 PM   #8
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,578
Rewards Points: 2,836
Default

Heat Pump A/C Performance Expectation


Insulating that pipe won't make a difference.

It can provide more heat when it low on charge then it can cooling. So you may be low on charge.
__________________
When posting in certain forums, knowing your location will help others give better feedback/advice/solutions to your questions.
beenthere is online now   Reply With Quote
Old 07-24-2014, 10:11 AM   #9
Newbie
 
Join Date: Jul 2014
Posts: 7
Rewards Points: 10
Default

Heat Pump A/C Performance Expectation


Thanks gang, I'll get it looked at!

J_Manson is offline   Reply With Quote
Reply

Tags
heat pump performance


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
dual fuel heat pump - no heat without propane sweetfarm HVAC 3 10-11-2012 08:07 AM
Electric baseboard VS Heat pump Mattme123 HVAC 20 09-21-2012 08:41 PM
Heat Pump Crisis Part II Doc Holliday HVAC 58 12-07-2011 09:14 PM
Comparison and Heat Pump Selection help... ChrisDIY HVAC 7 03-06-2010 08:34 PM
New Heat Pump..questions? ddave23 HVAC 4 03-05-2010 05:13 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.